Dmitri Mendeleev

I have no need of proof. The laws of nature, unlike the laws of grammar, admit of no exception.

Dmitri Ivanovich Mendeleev, Russian: Дми́трий Ива́нович Менделе́ев, also romanized Mendeleyev or Mendeleef (8 February [O.S. 27 January] 1834 – 2 February [O.S. 20 January] 1907) was a Russian chemist and inventor. He is credited as being the creator of the first version of the periodic table of elements. Using the table, he predicted the properties of elements yet to be discovered.

His stroke of genius was to leave gaps for elements that were still to be discovered, predicting what their properties should be from his table. This was a tremendous publicity coup! A few years later, new elements were discovered with properties which matched almost exactly with Mendeleev's predictions - the case was won...

When Mendeleev began teaching at the University, there were 63 known elements, each identified by atomic weights newly determined by Avagadro's hypothesis. He had to develop some system of classification. The two basic methods for dividing the elements—into metals and metalloids (nonmetals) or by using the new concept of valency—seemed unhelpful to Mendeleev. He chose to write his own textbook instead and work out the challenges of classification himself.

Michael D. Gordin, A Well-Ordered Thing: Dimitrii Mendeleev and the Shadow of the Periodic Table (2004)

Mendeleev was not concerned in 1869 with establishing a basic law of chemistry. He was concerned with writing a textbook for young chemists at St. Petersburg University. ...From 1871 on, Mendeleev himself would repeatedly abstract periodicity from its context... making it seem an emblem of pure science. ...it is how those sketches turned into an immutable law that requires explaining....Mendeleev's predictions themselves had naturalized periodicity by demonstrating the predictive power of his system. He then used this success to naturalize other components of the Great Reforms model.

Michael D. Gordin, A Well-Ordered Thing: Dimitrii Mendeleev and the Shadow of the Periodic Table (2004)

The distinction would only come to Mendeleev halfway through writing his Principles of Chemistry. ...chemical practice and not chemical theory had provided his initial organizing principle... Up to this point [Chapter 20], Mendeleev had only treated four elements in any detail: oxygen, carbon, nitrogen, and hydrogen—the so-called "organogens." Mendeleev began this chapter as usual by purifying the central substance, sodium chloride, from sources such as seawater. A discussion of sodium and chlorine followed in the next few chapters, and finally the halogens appeared... that were closely related to chlorine... and the alkali metals (the sodium family) form the first chapter of volume 2. ...he had dealt with only 8 elements, relegating 55... to the second volume. ...Mendeleev's earlier system of pedalogically useful organization—using laboratory practices... could no longer sustain the burden of exposition. He needed a new system... and he hit upon the idea of using a numerical marker for each element. Atomic weight seemed the most likely candidate for a system that would (a) account for all remaining elements; (b) do so in limited space; and (c) maintain some pedagogical merit. His solution, the periodic system, remains one of the most useful tools in chemistry.

Michael D. Gordin, A Well-Ordered Thing: Dimitrii Mendeleev and the Shadow of the Periodic Table (2004)

In writing a textbook of general chemistry, Mendeleev devoted separate chapters to families of elements with similar properties, including the alkali metals, the alkaline earth metals, and the halogens. Reflecting on the properties of these and other elements, he proposed in 1869 a primitive version of today's periodic table. Indeed, he predicted detailed properties for three such elements (scandium, gallium, and germanium). By 1886 all of these elements had been discovered and found to have properties very similar to those he had predicted.

"the elements tellurium and iodine occurred in the wrong order on the basis of their atomic weight"Mendeleev's 1869 Periodic Table

Mendeleev noticed that there were regular repeating patterns and similarities between different elements when they were ordered in terms of their atomic weights. Atomic weight was originally calculated from the average mass of one mole of the element relative to hydrogen (though the modern comparison is with carbon-12...). However, even Mendeleev was aware that classification based on atomic weight was flawed; for example, the elements tellurium and iodine occurred in the wrong order on the basis of their atomic weight, with iodine having a lower atomic weight but rightly having the properties of the halogen group (chlorine, fluorine, etc)... Mendeleev therefore decided to reverse the periodic sequence in their case. It was only in the twentieth century, when the structure of the atom based on the protons and the neutrons was identified, that the use of atomic number rather than atomic weight provided the ideal basis for the periodic table classification system. The atomic number of an element refers to its number of protons... Because the chemical properties of an element are determined by the number of negatively charged electrons, which in the non-ionozed form of the element matches the number of protons, there are many elements that have a number of isotopes, that is, have different numbers of neutrons, affecting the atomic weight but not the atomic number. Hence, Mendeleev's tellurium and iodine anomoly turned out to be because the tellurium he had sourced contained a preponderance of a heavier tellurium isotope giving it a greater atomic weight than idodine.

Mick Power, Madness Cracked (2014)

Despite Mendeleev's initial system being flawed, and the correct theoretical basis of the periodic table not being identified for another 50 years, Mendeleev was able to predict correctly a number of elements that had yet to be identified but which were expected to exist if the repeating periodic structure of the table was correct. These elements included gallium and germanium, whose properties Mendeleev had been able to outline because of their membership in groups of poor metals that included known elements such as aluminum and silicon, respectively (hence Mendeleev's original names of "eka-aluminum" for gallium and "eka-silicon" for germanium). One of the great strengths of a theoretically based classification system, therefore, is that it can predict the existence of yet-to-be identified members of the system or can lead to a reclassification of members that have been misclassified under previous systems.

Mick Power, Madness Cracked (2014)

Germanium, which name you should preserve since you are factually its father, is the element eka-silicon, Es-73, predicted by Mendeleev, the lowest homolog of tin, standing in the first large period between Ga (69.8) and As (79.9)... Eka-siicon is the element which we have awaited with great anticipation, and in any case the immediate study of germanium will be the most definitive experimentum crucis for the periodic system.

Dimitri was writing a textbook and wanted to organize the elements properly. So he wrote each element onto its own card to help him sort them out. Dimitri enjoyed playing cards, especially patience, and one evening he dosed off while working. He had a dream in which each of the cards lined up in rows, just like a game of patience. When he woke, he realized that he should put the elements in order of atomic mass.

David Sang, Lawrie Ryan, Jane Taylor, Scientifica: Raiders of the Lost Quadrat (2005)

Mendeleev... set about writing a book aimed at summarizing all of inorganic chemistry. It was while writing this book that he identified the organizing principle... the periodic system of the elements.

Eric R. Scerri, "The Story of the Periodic Table," Chemistry and Chemical Reactivity, Enhanced Edition ed. John Kotz, Paul Treichel, John Townsend (2009)

Dimitri Mendeleev was probably the greatest scientist produced by Russia. ...the periodic table was developed by Mendeleev, as well as five other scientists, over a period of about 10 years, after the Italian chemist Cannizzaro had published a consistent set of atomic weights in 1860. It appears that Mendeleev was unaware of the work of several of his co-discoverers, however. ...What is not well known is that about half of the elements that Mendeleev predicted were never found.

Eric R. Scerri, "The Story of the Periodic Table," Chemistry and Chemical Reactivity, Enhanced Edition ed. John Kotz, Paul Treichel, John Townsend (2009)

He formulated, as the fundamental law of the physico-chemical sciences, the dictum that "all the properties of bodies are periodic functions of their atomic weights"... on reaching this point of its development, the conception of Prof. Mendeleev becomes essentially injurious. Under the pretext of a law which has still to be demonstrated, it forbids us to throw light upon pure matters of observation, and forces us to remain in a vicious circle from which there is no escape. I think that it is time to show clearly that there is nothing [here] which merits the name of law or system.